Viscosity index improver and lubricant composition

Abstract

To provide a viscosity index improver and a lubricant composition having excellent shear stability and rolling friction coefficient.SOLUTION: A viscosity index improver comprises a copolymer (A) containing a polyolefin monomer (a) represented by general formula (1) and a polyfunctional monomer (c) having two or more ethylenic unsaturated groups in one molecule as essential constituent monomers, wherein the weight ratio (c / a) of the monomer (c) to the monomer (a) in the monomers constituting the copolymer (A) is 0.00001 to 0.00300.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to viscosity index improvers and lubricating oil compositions. [Background technology]

[0002] In recent years, there has been an increasing demand for fuel-efficient automobiles in order to reduce CO2 emissions and conserve oil resources. One way to reduce fuel consumption is to reduce viscous resistance by lowering the viscosity of engine oil. However, lowering the viscosity raises concerns about mechanical protection, such as leakage and seizure. The 0W-20 and 0W-16 grades in the US SAE engine oil viscosity standard (SAE J300) are stipulated to have a 150°C HTHS viscosity (ASTM D4683 or D5481) of 2.6 mPa·s and 2.3 mPa·s or higher, respectively, as the viscosity under high temperature and high shear (HTHS viscosity). To reduce fuel consumption, engine oils that meet the above viscosity standards and have lower HTHS viscosity in the effective temperature range of 80°C or 100°C are required. In addition, engine oils with good friction properties are required to reduce engine friction and wear. Therefore, a method of adding a viscosity index improver to a lubricating oil is widely used as a method of improving the viscosity characteristics. Known examples of such viscosity index improvers include methacrylic acid ester copolymers (Patent Documents 1 to 4), olefin copolymers (Patent Document 5), and macromonomer copolymers (Patent Document 6). However, the viscosity index improver containing the macromonomer copolymer has a problem that it does not have sufficient shear stability when added to an engine oil composition, and further has a problem that the oil film tends to thin at high temperatures and has a high friction coefficient in a rolling friction test. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2732187 [Patent Document 2] Patent No. 2941392 [Patent Document 3] Japanese Patent Application Publication No. 7-62372 [Patent Document 4] JP 2004-307551 A [Patent Document 5] JP 2005-200454 A [Patent Document 6] Special Publication No. 2008-546894 Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a viscosity index improver and lubricating oil composition that has good shear stability and rolling coefficient of friction (MTM coefficient of friction). [Means for solving the problem]

[0005] As a result of extensive investigations, the present inventors have arrived at the present invention. That is, the present invention relates to a viscosity index improver comprising a copolymer (A) having, as essential constituent monomers, a polyolefin monomer (a) represented by the following general formula (1) and a polyfunctional monomer (c) having two or more ethylenically unsaturated groups in one molecule, wherein the weight ratio (c / a) of the monomer (c) to the weight of the monomer (a) among the monomers constituting the copolymer (A) is 0.00001 to 0.00300; and a lubricating oil composition comprising the viscosity index improver and a base oil.

[0006] [ka] [In general formula (1), R 1 is a hydrogen atom or a methyl group; -X 1 - is -O-, -O(AO) m - or -NH-, where A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different; R 2is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; and p is the number 0 or 1. Effect of the Invention

[0007] The viscosity index improver of the present invention exhibits the effects of being excellent in shear stability and rolling friction coefficient (MTM friction coefficient). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The viscosity index improver of the present invention is a viscosity index improver comprising a copolymer (A) having, as essential constituent monomers, a polyolefin monomer (a) represented by the following general formula (1) and a polyfunctional monomer (c) having two or more ethylenically unsaturated groups in one molecule, wherein the weight ratio (c / a) of the monomer (c) to the weight of the monomer (a) among the monomers constituting the copolymer (A) is 0.00001 to 0.00300. Copolymers containing monomer (a) as a constituent monomer tend to have insufficient shear stability. However, in the present invention, it has been found that by using polyfunctional monomer (c) in the above weight ratio (c / a), it is possible to obtain a copolymer having excellent shear stability without affecting the function as a viscosity index improver (viscosity index improving effect, HTHS viscosity, etc.), and furthermore, it is possible to reduce the rolling friction coefficient.

[0009] [ka] [In general formula (1), R 1 is a hydrogen atom or a methyl group; -X 1 - is -O-, -O(AO) m - or -NH-, where A is an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 10, and when m is 2 or more, A may be the same or different; R 2 is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; and p is the number 0 or 1.

[0010] In the present invention, the copolymer (A) contains, as essential constituent monomers, a polyolefin monomer (a) represented by the above general formula (1), a monomer (b) represented by the above general formula (2), and a polyfunctional monomer (c).

[0011] The polyolefin monomer (a) represented by the above general formula (1) will now be described. R in general formula (1) 1 is a hydrogen atom or a methyl group. Among these, the methyl group is preferred from the viewpoint of the viscosity index improving effect.

[0012] -X in general formula (1) 1 - is -O-, -O(AO) m - or -NH-. A is an alkylene group having 2 to 4 carbon atoms, and examples thereof include an ethylene group, a 1,2- or 1,3-propylene group, an isobutylene group, and a 1,2-, 1,3-, or 1,4-butylene group. AO is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include an ethyleneoxy group, a 1,2- or 1,3-propyleneoxy group, an isobutyleneoxy group, and a 1,2-, 1,3-, or 1,4-butyleneoxy group. m is the number of moles of alkylene oxide added and is an integer of 1 to 10, and is preferably an integer of 1 to 4, and more preferably an integer of 1 to 2, from the viewpoint of the viscosity index improving effect. When m is 2 or more, A may be the same or different, (AO) m The moieties may be bonded in a random or block fashion. -X 1 Among these, -O- and -O(AO) are preferred from the viewpoint of improving the viscosity index. m and more preferably, -O- and -O(CH2CH2O)1-. p is a number of 0 or 1.

[0013] R in general formula (1) 2is a residue in which one hydrogen atom has been removed from a hydrocarbon polymer that contains a 1,2-butylene group (-CH2CH(CH2CH3)- or -CH(CH2CH3)CH2-) as a structural unit. In a hydrocarbon polymer containing 1,2-butylene groups as a structural unit, the ratio of 1,2-butylene groups in all structural units is preferably 10 to 90 mol %, more preferably 20 to 80 mol %, from the viewpoint of HTHS viscosity at 100°C. When two types of hydrocarbon polymers containing 1,2-butylene groups as a constituent unit and having different ratios of 1,2-butylene groups are used in combination, the absolute value of the difference in the ratios of the two types of 1,2-butylene groups is preferably 10 to 80 mol %, and more preferably 20 to 70 mol %, from the viewpoint of low-temperature viscosity.

[0014] The hydrocarbon polymer containing a 1,2-butylene group as a constituent unit is preferably one having 37 or more carbon atoms, and examples thereof include a polymer using 1-butene as a constituent monomer (unsaturated hydrocarbon (x)) and a polymer obtained by hydrogenating the carbon-carbon double bond of a 1,2-adduct of a polymer using 1,3-butadiene.

[0015] Regarding the structure derived from 1-butene and / or 1,3-butadiene of the hydrocarbon polymer in the general formula (1), the ratio of 1,2-butylene groups in all constitutional units is 13 Specifically, for example, when only monomers having four carbon atoms are used, the hydrocarbon polymer can be 13 It can be determined by C-NMR analysis and calculation using the following mathematical formula (1). 13 In C-NMR, a peak derived from the tertiary carbon atom (-CH2CH(CH2CH3)-) of the branched methylene group of the 1,2-butylene group appears at an integral value (integral value B) of 26 to 27 ppm. The ratio of 1,2-butylene groups can be calculated from the integral value of the above peak and the integral value of the peak of all carbons in the hydrocarbon polymer (integral value C). Ratio of 1,2-butylene groups (mol%) = {(integral value B) × 4} / (integral value C) × 100 (1) In order to increase the ratio of 1,2-butylene groups, for example, in anionic polymerization using 1,3-butadiene, the reaction temperature should be lowered to a temperature not higher than the boiling point of 1,3-butadiene (-4.4°C) and the amount of polymerization initiator added should be reduced relative to the 1,3-butadiene. In order to decrease the ratio of 1,2-butylene, the reaction temperature should be increased to a temperature not lower than the boiling point of 1,3-butadiene and the amount of polymerization initiator added should be increased relative to the 1,3-butadiene.

[0016] R in general formula (1) 2 From the viewpoint of the viscosity index improving effect, the ratio of 1,3-butadiene to all the monomers constituting the copolymer (the weight ratio of 1,3-butadiene to all the monomers constituting the copolymer, in a hydrocarbon polymer containing 1,2-butylene groups as a constituent unit) is preferably 50% by weight or more, more preferably 75% by weight or more, particularly preferably 85% by weight or more, and most preferably 90% by weight or more.

[0017] R in general formula (1) 2 In the 1,3-butadiene-derived structure constituting a part or all of the above, the molar ratio of 1,2-butylene groups (1,2-adduct) to 1,4-butylene groups (1,4-adduct) (1,2-adduct / 1,4-adduct) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, and particularly preferably 20 / 80 to 80 / 20, from the viewpoints of the viscosity index improving effect and low-temperature viscosity. As the monomer (a), it is preferable to use a monomer having a molar ratio (1,2-adduct / 1,4-adduct) of 1 / 99 to 50 / 50 in combination with a monomer having a molar ratio of 51 / 49 to 99 / 1, and it is more preferable to use a monomer having a molar ratio of 10 / 90 to 50 / 50 in combination with a monomer having a molar ratio of 55 / 45 to 90 / 10 in combination. R in general formula (1) 2 The molar ratio of 1,2-adduct to 1,4-adduct in the 1,3-butadiene-derived structure that constitutes part or all of 1 H-NMR and 13 It can be measured by C-NMR, Raman spectroscopy, etc.

[0018] R in general formula (1) 2From the viewpoint of low temperature viscosity, it is preferable that is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing an isobutylene group as a constituent unit in addition to a 1,2-butylene group. A method for obtaining a hydrocarbon polymer containing an isobutylene group as a constituent unit includes a method of using isobutene as a constituent monomer (unsaturated hydrocarbon (x)). The total ratio of isobutylene groups and 1,2-butylene groups in the hydrocarbon polymer is preferably 30 mol % or more, more preferably 40 mol % or more, particularly preferably 50 mol % or more, and most preferably 60 mol % or more, based on the total number of moles of the constituent units of the hydrocarbon polymer, from the viewpoint of low-temperature viscosity.

[0019] Based on the total number of structural units of the hydrocarbon polymer, the total ratio of isobutylene groups and 1,2-butylene groups is 13 It can be determined by analyzing the monomer by C-nuclear magnetic resonance spectroscopy and calculating using the following formula (2). Specifically, for example, when only monomers having four carbon atoms are used, 13 In the C-nuclear magnetic resonance spectrum, a peak derived from the methyl group of the isobutylene group appears at an integral value of 30-32 ppm (integral value A), and a peak derived from the tertiary carbon atom of the branched methylene group of the 1,2-butylene group appears at an integral value of 26-27 ppm (integral value B). It can be calculated from the integral value of the above peaks and the integral value of the peak of all carbon in the hydrocarbon polymer (integral value C). Total ratio of isobutylene groups and 1,2-butylene groups (mol%) = {(integral value A) × 2 + (integral value B) × 4} / (integral value C) × 100 (2)

[0020] The hydrocarbon polymer containing 1,2-butylene as a constituent unit may contain the following (1) to (3) as the unsaturated hydrocarbon (x) as constituent monomers in addition to 1-butene and 1,3-butadiene. (1) Aliphatic unsaturated hydrocarbons [olefins having 2 to 36 carbon atoms (e.g., ethylene, propylene, 2-butene, isobutene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, triacosene, hexatriacosene, etc.) and dienes having 4 to 36 carbon atoms (e.g., isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.)] (2) Alicyclic unsaturated hydrocarbons [e.g., cyclohexene, (di)cyclopentadiene, pinene, limonene, indene, vinylcyclohexene, ethylidenebicycloheptene, etc.] (3) Aromatic group-containing unsaturated hydrocarbons (e.g., styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylbenzene, vinylnaphthalene, divinylbenzene, divinyltoluene, divinylxylene, and trivinylbenzene). The hydrocarbon polymer formed by these may be a block polymer or a random polymer. When the hydrocarbon polymer has carbon-carbon double bonds, the double bonds may be partially or entirely hydrogenated by hydrogenation. In one embodiment, R 2 The hydrocarbon polymer in may be a hydrocarbon polymer using only monomers having 4 carbon atoms as constituent monomers, and the monomers having 4 carbon atoms may be 1-butene and / or 1,3-butadiene, and may contain isobutene as necessary. The weight proportion of unsaturated hydrocarbons other than 1-butene, 1,3-butadiene and isobutene in the monomer (a) is preferably 50% by weight or less, more preferably 25% by weight or less, next more preferably 15% by weight or less, particularly preferably 10% by weight or less.

[0021] The weight average molecular weight (hereinafter abbreviated as Mw) and number average molecular weight (hereinafter abbreviated as Mn) of the monomer (a) can be measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions. <Measurement conditions for Mw and Mn of monomer (a)> Equipment: "HLC-8320GPC" [Tosoh Corporation] Column: "TSKgel GMHXL" [Tosoh Corporation] x 2 "TSKgel Multipore H XL-M" [Manufactured by Tosoh Corporation] 1 piece Measurement temperature: 40℃ Sample solution: 0.25% by weight tetrahydrofuran solution Solution injection volume: 10.0μl Detector: Refractive index detector Reference material: Standard polystyrene (TS Reference material: Standard polystyrene (TSKstandard POLYSTYRENE)) 12 points (molecular weight: 589, 1,050, 2,630, 9,100, 19,500, 37,900, 96,400, 190,000, 355,000, 1,090,000, 2,110,000, 4,480,000) [Tosoh Corporation]

[0022] The Mn of the monomer (a) is preferably from 800 to 10,000, more preferably from 1,000 to 9,000, and particularly preferably from 1,200 to 8,500. When the Mn of the monomer (a) is 800 or more, the viscosity index improving effect tends to be good, and when it is 10,000 or less, the shear stability during long-term use tends to be good. From the viewpoint of low-temperature viscosity, the Mw of the monomer (a) is preferably from 900 to 13,000, more preferably from 1,200 to 12,000, and particularly preferably from 1,500 to 11,000.

[0023] Monomer (a) can be obtained by an esterification reaction between polymer (Y) containing a hydroxyl group at one end obtained by introducing a hydroxyl group into one end of a hydrocarbon polymer and (meth)acrylic acid, or by an ester exchange reaction between polymer (Y) and an alkyl (meth)acrylate ester (preferably an alkyl group having 1 to 4 carbon atoms) such as methyl (meth)acrylate. Incidentally, "(meth)acrylic" means "acrylic and / or methacrylic".

[0024] The solubility parameter (hereinafter abbreviated as SP value) of the constituent unit derived from the monomer (a) (a structure in which the vinyl group portion of the monomer (a) has reacted to form a single bond) is preferably 7.0 to 9.0 (cal / cm) from the viewpoint of solubility in the lubricating oil. 3 ) 1 / 2 and more preferably 7.3 to 8.5 (cal / cm 3 ) 1 / 2 It is. The SP value in the present invention is a value calculated by the method described in formula (28) on page 153 of the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, pp. 147-154) using the values ​​(heat of vaporization and molar volume at 25°C of atoms or functional groups) described on page 152 (Table. 5) of the same. Specifically, the Δe i and Δv i It can be calculated by applying the values ​​corresponding to the types of atoms and atomic groups in the molecular structure to the following formula. SP value = (ΣΔe i / ΣΔv i ) 1 / 2

[0025] [Table 1] The SP value of the constituent unit derived from the monomer (a) can be calculated using the above parameters based on the molecular structure of the constituent unit derived from the monomer (a), and can be adjusted to a desired range by appropriately adjusting the monomer (unsaturated hydrocarbon (x)) and weight fraction used.

[0026] Specific examples of the polymer (Y) containing a hydroxyl group at one end include the following (Y1) to (Y4). Alkylene oxide adduct (Y1): a compound obtained by adding an alkylene oxide (ethylene oxide, propylene oxide, etc.) to a polymer obtained by polymerizing an unsaturated hydrocarbon (x) in the presence of an ionic polymerization catalyst (lithium catalyst, sodium catalyst, etc.) (in the general formula (1), -X 1 -ga-(AO) m - and p=0). Hydroboration product (Y2): a hydroboration product of a polymer of an unsaturated hydrocarbon (x) having a double bond at one end (e.g., those described in U.S. Pat. No. 4,316,973) (in the general formula (1), -X 1 - is -O- and p=0). Maleic anhydride-ene-aminoalcohol adduct (Y3); a product obtained by imidizing a reaction product obtained by an ene reaction between a polymer of an unsaturated hydrocarbon (x) having a double bond at one end and maleic anhydride with an aminoalcohol (in the general formula (1), -X 1 - is -O- and p=1). Hydroformyl hydrogenation product (Y4): a product obtained by hydroformylating a polymer of an unsaturated hydrocarbon (x) having a double bond at one end, followed by hydrogenation (e.g., the product described in JP-A-63-175096) (in the general formula (1), -X 1 - is -O- and p=0). Among these polymers (Y) containing a hydroxyl group at one end, from the viewpoint of the effect of improving the HTHS viscosity and the viscosity index, the alkylene oxide adduct (Y1), the hydroboronate (Y2) and the maleic anhydride-ene-amino alcohol adduct (Y3) are preferred, and the alkylene oxide adduct (Y1) is more preferred.

[0027] The polyfunctional monomer (c) having two or more ethylenically unsaturated groups in one molecule will now be described. In the polyfunctional monomer (c), examples of the ethylenically unsaturated group include a vinyl group, a (meth)acryloyl group, and an allyl group. Of these, a (meth)acryloyl group is preferred from the viewpoint of improving shear stability. In the polyfunctional monomer (c), the number of ethylenically unsaturated groups in one molecule is preferably 2 to 4, and more preferably 2, from the viewpoint of improving the shear stability.

[0028] Preferred examples of the polyfunctional monomer (c) include aliphatic di(meth)acrylates and aromatic ring-containing di(meth)acrylates. Examples of the aliphatic di(meth)acrylate include di(meth)acrylate of an alkanediol, and alicyclic di(meth)acrylate. Examples of alkanediol di(meth)acrylates include ethylene glycol diacrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, and 1,12-dodecanediol dimethacrylate.

[0029] Examples of the alicyclic di(meth)acrylate include dimethyloltricyclodecane diacrylate, cyclohexanedimethanol di(meth)acrylate, isobornyl di(meth)acrylate, adamantyl di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate.

[0030] Examples of aromatic ring-containing di(meth)acrylates include ethylene oxide adduct diacrylate of bisphenol A and propylene oxide adduct diacrylate of bisphenol A.

[0031] As the polyfunctional monomer (c), from the viewpoint of improving shear stability, an alicyclic di(meth)acrylate is preferred, more preferably cyclohexanedimethanol di(meth)acrylate, isobornyl di(meth)acrylate, adamantyl di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, even more preferably cyclohexanedimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and particularly preferably tricyclodecane dimethanol di(meth)acrylate.

[0032] In the present invention, the copolymer (A) may contain, as constituent monomers, a monomer (b) represented by the following general formula (2), a (meth)acrylic acid alkyl ester monomer (d) having an alkyl group with 1 to 4 carbon atoms, and a (meth)acryloyl monomer (e) having an alkyl group with 9 to 36 carbon atoms. From the viewpoint of viscosity index improvement effect, a copolymer containing the monomer (d) as a constituent monomer is preferred. From the viewpoint of solubility in base oil, a copolymer containing the monomer (e) as a constituent monomer is preferred.

[0033] The monomer (b) represented by the following general formula (2) will be described below.

[0034] [ka] [In general formula (2), R 3 is a hydrogen atom or a methyl group; -X 2 - is a group represented by -O- or -NH-; R 4 is an alkylene group having 2 to 4 carbon atoms; R 5 is an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms; q is an integer of 1 to 20, and when q is 2 or more, R 4 may be the same or different.]

[0035] R in general formula (2) 3 is a hydrogen atom or a methyl group. Among these, from the viewpoint of the viscosity index improving effect, a methyl group is preferred.

[0036] -X in formula (2) 2 - is a group represented by -O- or -NH-. Among these, from the viewpoint of the viscosity index improving effect, the group represented by -O- is preferred.

[0037] R in general formula (2) 4 is an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, a 1,2- or 1,3-propylene group, an isobutylene group, and a 1,2-, 1,3- or 1,4-butylene group. R 4 O is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include an ethyleneoxy group, a 1,2- or 1,3-propyleneoxy group, an isobutyleneoxy group, and a 1,2-, 1,3-, or 1,4-butyleneoxy group. In the general formula (2), q is an integer of 1 to 20, and from the viewpoints of the viscosity index improving effect and low-temperature viscosity, it is preferably an integer of 1 to 5, and more preferably an integer of 1 or 2. R when q is 2 or more 4 O may be the same or different, (R 4 O) q The moieties may be bonded in a random or block fashion.

[0038] R in general formula (2) 5 is an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms. The alkyl group includes linear or branched alkyl groups, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a s-butyl group, a t-butyl group, an n-heptyl group, an isoheptyl group, an n-hexyl group, a 2-ethylhexyl group, an n-pentyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, and an n-octadecyl group. Examples of the aryl group include a phenyl group, a naphthyl group, an anthracenyl group, and groups in which at least one of the aromatic hydrogen atoms of these groups is substituted with an alkyl group having 1 to 14 carbon atoms. Of the alkyl groups having 1 to 18 carbon atoms and the aryl groups having 6 to 20 carbon atoms, from the viewpoint of the viscosity index improving effect, preferred are alkyl groups having 1 to 7 carbon atoms, more preferred are alkyl groups having 1 to 6 carbon atoms, particularly preferred are alkyl groups having 1 to 5 carbon atoms, and most preferred are alkyl groups having 2 or 4 carbon atoms.

[0039] Specific examples of the monomer (b) include methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, pentyloxyethyl (meth)acrylate, hexyloxyethyl (meth)acrylate, heptyloxyethyl (meth)acrylate, octyloxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, propoxypropyl (meth)acrylate, butoxypropyl (meth)acrylate, pentyloxypropyl (meth)acrylate, hexyloxypropyl (meth)acrylate, heptyloxypropyl (meth)acrylate, and octyloxypropyl. Examples of the acrylates include (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, propoxybutyl (meth)acrylate, butoxybutyl (meth)acrylate, pentyloxybutyl (meth)acrylate, hexyloxybutyl (meth)acrylate, heptyloxybutyl (meth)acrylate, and octyloxybutyl (meth)acrylate, as well as esters of (meth)acrylic acid and a compound obtained by adding 2 to 20 moles of an alkylene oxide having 2 to 4 carbon atoms (at least one selected from the group consisting of ethylene oxide, propylene oxide, and butylene oxide) to an alkyl alcohol having 1 to 18 carbon atoms or an aryl alcohol having 6 to 20 carbon atoms (e.g., phenol, etc.). Among the monomers (b), ethoxyethyl (meth)acrylate and butoxyethyl (meth)acrylate are preferred from the viewpoint of the viscosity index improving effect.

[0040] The monomer (d) is a (meth)acryloyl monomer having an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, and a t-butyl group.

[0041] Examples of the (meth)acrylic acid alkyl ester monomer (d) having an alkyl group having 1 to 4 carbon atoms include esters of linear or branched alcohols having 1 to 4 carbon atoms and (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, s-butyl (meth)acrylate, and isobutyl (meth)acrylate. Among the monomers (d), from the viewpoint of the viscosity index improving effect, methyl (meth)acrylate, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl (meth)acrylate and n-butyl (meth)acrylate are particularly preferred.

[0042] The monomer (e) is other than the monomer (b), and includes a (meth)acryloyl monomer (e1) having a linear alkyl group having 9 to 36 carbon atoms, and a (meth)acryloyl monomer (e2) having a branched alkyl group having 9 to 36 carbon atoms, represented by the following general formula (4), and the like. The monomer (e) may be used alone or in combination of two or more kinds.

[0043] [ka] [In general formula (4), R 8 is a hydrogen atom or a methyl group; -X 4 - is a group represented by -O- or -NH-; R9 O is an alkyleneoxy group having 2 to 4 carbon atoms; R 10 and R 11 are each independently a linear alkyl group having 1 to 24 carbon atoms, R 10 and R 11 The total number of carbon atoms in R is 7 to 34; s is an integer from 0 to 20, and when s is 2 or more, 9 O may be the same or different.

[0044] Examples of the (meth)acryloyl monomer (e1) having a linear alkyl group having 9 to 36 carbon atoms (hereinafter sometimes abbreviated as monomer (e1)) include (meth)acrylic acid alkyl esters {an ester of a linear alkyl alcohol having 9 to 36 carbon atoms and (meth)acrylic acid, such as n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-penta(meth)acrylate, n-butyl ( ... decyl, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-icosyl (meth)acrylate, n-tetracosyl (meth)acrylate, n-triacontyl (meth)acrylate, and n-hexatriacontyl (meth)acrylate}, esters of (meth)acrylic acid with an adduct of 1 to 20 moles of an alkylene oxide (having 2 to 4 carbon atoms) of a linear alkyl alcohol having 9 to 36 carbon atoms, and (meth)acrylic acid alkylamides {amides of linear alkylamines having 9 to 36 carbon atoms and acrylic acid, etc.}. Among the monomers (e1), from the viewpoint of the viscosity index improving effect, preferred are (meth)acrylic acid alkyl esters having a linear alkyl group having 12 to 28 carbon atoms, more preferred are (meth)acrylic acid esters having a linear alkyl group having 12 to 24 carbon atoms, and particularly preferred are (meth)acrylic acid esters having a linear alkyl group having 12 to 20 carbon atoms. The monomer (e1) may be used alone or in combination of two or more kinds.

[0045] In the monomer (e2), R in the general formula (4) 8is a hydrogen atom or a methyl group. Among these, from the viewpoint of the viscosity index improving effect, a methyl group is preferred. -X in formula (4) 4 - is a group represented by -O- or -NH-. Among these, from the viewpoint of the viscosity index improving effect, the group represented by -O- is preferred. R in general formula (4) 9 is an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, a 1,2- or 1,3-propylene group, an isobutylene group, and a 1,2-, 1,3-, or 1,4-butylene group. R 9 O is an alkyleneoxy group having 2 to 4 carbon atoms, and examples thereof include an ethyleneoxy group, a 1,2- or 1,3-propyleneoxy group, an isobutyleneoxy group, and a 1,2-, 1,3-, or 1,4-butyleneoxy group.

[0046] In the general formula (4), s is an integer of 0 to 20, and from the viewpoint of the effect of improving the viscosity index, an integer of 0 to 5 is preferable, and an integer of 0 to 2 is more preferable. R when s is 2 or more 9 O may be the same or different, (R 9 O) s The moieties may be randomly or block bonded.

[0047] R in general formula (4) 10 and R 11 are each independently a linear alkyl group having 1 to 24 carbon atoms. Specific examples include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-heptyl group, an n-hexyl group, an n-pentyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tetradecyl group, an n-hexadecyl group, an n-octadecyl group, an n-eicosyl group, and an n-tetracosyl group. Among the linear alkyl groups having 1 to 24 carbon atoms, preferred from the viewpoint of the viscosity index improving effect are R 10 or R 11 At least one of R is a linear alkyl group having 6 to 24 carbon atoms, and more preferably R 10or R 11 At least one of R is a linear alkyl group having 6 to 20 carbon atoms. 10 or R 11 At least one of them is a linear alkyl group having 8 to 16 carbon atoms. R 10 and R 11 The total number of carbon atoms is 7 to 34, and from the viewpoint of the viscosity index improving effect, it is preferably 12 to 30, and more preferably 14 to 26. R 10 and R 11 The carbon chain containing R 10 and R 11 The branched alkyl group has 9 to 36 carbon atoms, and from the viewpoint of the viscosity index improving effect, it preferably has 14 to 32 carbon atoms, and more preferably has 16 to 28 carbon atoms.

[0048] Specific examples of the monomer (e2) include 2-octyldecyl (meth)acrylate, an ester of ethylene glycol mono-2-octylpentadecyl ether and (meth)acrylic acid, 2-n-octyldodecyl (meth)acrylate, 2-n-decyltetradecyl (meth)acrylate, 2-n-dodecylhexadecyl (meth)acrylate, 2-n-tetradecyloctadecyl (meth)acrylate, 2-n-tetradecyloctadecyl (meth)acrylate, and 2-n- Dodecylpentadecyl, 2-n-tetradecylheptadecyl (meth)acrylate, 2-n-hexadecylheptadecyl (meth)acrylate, 2-n-heptadecylicosyl (meth)acrylate, 2-n-hexadecyldocosyl (meth)acrylate, 2-n-eicosyldocosyl (meth)acrylate, 2-n-tetracosylhexacosyl (meth)acrylate, and N-2-octyldecyl (meth)acrylamide. The monomer (e2) may be used alone or in combination of two or more kinds.

[0049] Among the monomers (e), from the viewpoints of solubility in base oil and low-temperature viscosity, preferred is a (meth)acryloyl monomer (e2) having a branched alkyl group having 9 to 36 carbon atoms, represented by the above general formula (4), more preferred is a (meth)acryloyl monomer having a branched alkyl group having 14 to 32 carbon atoms, and particularly preferred is a (meth)acryloyl monomer having a branched alkyl group having 16 to 28 carbon atoms, among the monomers (e2).

[0050] The copolymer (A) in the present invention may further contain, in addition to the above-mentioned monomers (a) to (e), a nitrogen atom-containing monomer (f), a hydroxyl group-containing monomer (g), a phosphorus atom-containing monomer (h), an aromatic ring-containing vinyl monomer (i), and monomers (j) to (n) as constituent monomers. The monomers (f) to (n) may each be used alone or in combination of two or more.

[0051] The nitrogen atom-containing monomer (f) includes the following monomers (f1) to (f4) excluding the monomers (a) to (e).

[0052] Amide group-containing monomer (f1): (Meth)acrylamide, N-methyl(meth)acrylamide, N-(N'-monoalkylaminoalkyl)(meth)acrylamide [one having an aminoalkyl group (having 2 to 6 carbon atoms) with one alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-(N'-methylaminoethyl)(meth)acrylamide, N-(N'-ethylaminoethyl)(meth)acrylamide, N-(N'-isopropylamino-n-butyl)(meth)acrylamide, and N-(N'-n- or isobutylamino-n-butyl)(meth)acrylamide, etc.], dialkyl(meth)acrylamide [one having two alkyl groups having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, etc.] acrylamide and N,N-di-n-butyl(meth)acrylamide, etc.], N-(N',N'-dialkylaminoalkyl)(meth)acrylamide [one having an aminoalkyl group (having 2 to 6 carbon atoms) in which two alkyl groups having 1 to 4 carbon atoms are bonded to the nitrogen atom of the aminoalkyl group; for example, N-(N',N'-dimethylaminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide and N-(N',N'-di-n-butylaminobutyl)(meth)acrylamide, etc.]; N-vinyl carboxylic acid amide [N-vinyl formamide, N-vinyl acetamide, N-vinyl propionic acid amide and N-vinyl hydroxyacetamide, etc.].

[0053] Nitro group-containing monomer (f2): Examples include 4-nitrostyrene.

[0054] Monomers containing primary to tertiary amino groups (f3): Primary amino group-containing monomers {alkenylamines having 3 to 6 carbon atoms [(meth)allylamine and crotylamine, etc.], aminoalkyl (meth)acrylates having 2 to 6 carbon atoms [aminoethyl (meth)acrylate, etc.]}; secondary amino group-containing monomers {monoalkylaminoalkyl (meth)acrylates [aminoalkyl groups having 2 to 6 carbon atoms with one alkyl group having 1 to 6 carbon atoms bonded to a nitrogen atom; for example, Nt-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.], dialkenylamines having 6 to 12 carbon atoms [di(meth)allylamine, etc.]}; tertiary amino group-containing monomers {dialkylaminoalkyl (meth)acrylates [aminoalkyl groups having 1 to 6 carbon atoms bonded to a nitrogen atom; for example, Nt-butylaminoethyl (meth)acrylate and N-methylaminoethyl (meth)acrylate, etc.] Examples of such monomers include those having an aminoalkyl group (having 2 to 6 carbon atoms) to which two alkyl groups are bonded; for example, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.], alicyclic (meth)acrylates having a nitrogen atom [morpholinoethyl (meth)acrylate, etc.], aromatic monomers [N-(N',N'-diphenylaminoethyl)(meth)acrylamide, N,N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone, N-vinylthiopyrrolidone, etc.]}, and their hydrochlorides, sulfates, phosphates, or lower alkyl (having 1 to 8 carbon atoms) monocarboxylate (acetic acid, propionic acid, etc.) salts.

[0055] Nitrile group-containing monomers (f4): (Meth)acrylonitrile and the like.

[0056] Among the monomers (f), preferred are the amide group-containing monomer (f1) and the primary to tertiary amino group-containing monomer (f3), and more preferred are N-(N',N'-diphenylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminoethyl)(meth)acrylamide, N-(N',N'-diethylaminoethyl)(meth)acrylamide, N-(N',N'-dimethylaminopropyl)(meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and N,N-diethylaminoethyl (meth)acrylate.

[0057] Hydroxyl-containing monomer (g): Hydroxyl-containing aromatic monomers (e.g., p-hydroxystyrene), hydroxyalkyl (C2-6) (meth)acrylates [2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, etc.], mono- or bis-hydroxyalkyl (C1-4) substituted (meth)acrylamides [N,N-bis(hydroxymethyl)(meth)acrylamide, N,N-bis(hydroxypropyl)(meth)acrylamide, N,N-bis(2-hydroxybutyl)(meth)acrylamide, etc.], vinyl alcohol, alkenols having 3 to 12 carbon atoms [(meth)allyl alcohol, crotyl alcohol, alcohol, isocrotyl alcohol, 1-octenol, 1-undecenol, etc.], alkene monools or alkene diols having 4 to 12 carbon atoms [1-buten-3-ol, 2-buten-1-ol, 2-buten-1,4-diol, etc.], hydroxyalkyl (having 1 to 6 carbon atoms) alkenyl (having 3 to 10 carbon atoms) ethers (2-hydroxyethylpropenyl ether, etc.), alkenyl (having 3 to 10 carbon atoms) ethers or (meth)acrylates of polyhydric (trihydric) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, sugars, sucrose, etc.) [sucrose (meth)allyl ether, etc.], etc.; Examples thereof include polyoxyalkylene glycols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 50), polyoxyalkylene polyols [polyoxyalkylene ethers of the above-mentioned tri- to octahydric alcohols (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 100), etc.], mono(meth)acrylates of alkyl (carbon number 1 to 4) ethers of polyoxyalkylene glycols or polyoxyalkylene polyols [polyethylene glycol (Mn: 100 to 300) mono(meth)acrylate, polypropylene glycol (Mn: 130 to 500) mono(meth)acrylate, methoxypolyethylene glycol (Mn: 110 to 310) (meth)acrylate, lauryl alcohol ethylene oxide adduct (2 to 30 mol) (meth)acrylate, polyoxyethylene mono(meth)acrylate (Mn: 150 to 230) sorbitan, etc.].

[0058] Examples of the phosphorus atom-containing monomer (h) include the following monomers (h1) to (h2).

[0059] Phosphate ester group-containing monomer (h1): Examples of such phosphates include (meth)acryloyloxyalkyl (carbon number 2 to 4) phosphate esters [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and alkenyl phosphate esters [vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, dodecenyl phosphate, etc.]. Note that "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

[0060] Phosphono group-containing monomer (h2): Examples thereof include (meth)acryloyloxyalkyl (C2-4) phosphonic acids [(meth)acryloyloxyethyl phosphonic acid, etc.] and alkenyl (C2-12) phosphonic acids [vinyl phosphonic acid, allyl phosphonic acid, octenyl phosphonic acid, etc.].

[0061] Among the monomers (h), preferred are phosphate group-containing monomers (h1), more preferred are (meth)acryloyloxyalkyl (carbon number: 2 to 4) phosphate esters, and particularly preferred is (meth)acryloyloxyethyl phosphate.

[0062] Aromatic ring-containing vinyl monomer (i): Examples of the vinyl styrene include styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, 4-crotylbenzene, indene, and 2-vinylnaphthalene.

[0063] Of the monomers (i), styrene and α-methylstyrene are preferred, and styrene is more preferred.

[0064] Examples of the monomer (j) having two or more unsaturated groups include divinylbenzene, alkadienes having 4 to 12 carbon atoms (such as butadiene, isoprene, 1,4-pentadiene, 1,6-heptadiene, and 1,7-octadiene), (di)cyclopentadiene, vinylcyclohexene, and ethylidene bicycloheptene, limonene, ethylene di(meth)acrylate, polyalkylene oxide glycol di(meth)acrylate, pentaerythritol triallyl ether, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, and esters of unsaturated carboxylic acids and glycols having an Mn of 500 or more and esters of unsaturated alcohols and carboxylic acids, as described in International Publication WO01 / 009242.

[0065] Vinyl esters, vinyl ethers, vinyl ketones (k) (sometimes abbreviated as monomer (k)): Examples of the vinyl esters include vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octanoate, etc.), alkyl, aryl, or alkoxyalkyl vinyl ethers having 1 to 12 carbon atoms (methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, 2-ethylhexyl vinyl ether, phenyl vinyl ether, vinyl-2-methoxyethyl ether, vinyl-2-butoxyethyl ether, etc.), and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl ketone, etc.).

[0066] Epoxy group-containing monomer (l) (sometimes abbreviated as monomer (l)): Examples include glycidyl (meth)acrylate and glycidyl (meth)allyl ether.

[0067] Halogen-containing monomer (m) (sometimes abbreviated as monomer (m)): Examples include vinyl chloride, vinyl bromide, vinylidene chloride, (meth)allyl chloride, and halogenated styrenes (such as dichlorostyrene).

[0068] Esters of unsaturated polycarboxylic acids (n) (sometimes abbreviated as monomer (n)): Examples of the alkyl, cycloalkyl, or aralkyl esters of unsaturated polycarboxylic acids include C1-8 alkyl diesters of unsaturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.) (dimethyl maleate, dimethyl fumarate, diethyl maleate, dioctyl maleate, etc.).

[0069] In the copolymer (A), the weight proportion of the monomer (a) among the constituent monomers of the copolymer (A) is preferably 1 to 20% by weight, more preferably 8 to 18% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoints of the HTHS viscosity at 100°C, the kinematic viscosity at 40°C, the shear stability, the rolling friction coefficient (MTM friction coefficient) and the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (b) among the constituent monomers of the copolymer (A) is preferably 1 to 35% by weight, more preferably 1 to 20% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoints of the HTHS viscosity at 100°C, the kinematic viscosity at 40°C, the shear stability, the rolling friction coefficient (MTM friction coefficient) and the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (c) among the constituent monomers of the copolymer (A) is preferably 0.00001 to 0.060% by weight, and more preferably 0.0001 to 0.035% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoints of the effect of improving shear stability and the rolling friction coefficient (MTM friction coefficient). In the copolymer (A), the weight ratio (c / a) of the monomer (c) to the weight of the monomer (a) in the monomers constituting the copolymer (A) is 0.00001 to 0.00300, and from the viewpoint of improving the shear stability and the rolling friction coefficient (MTM friction coefficient), it is preferably 0.00005 to 0.00200, more preferably 0.00007 to 0.00100. If the weight ratio (c / a) is less than 0.00001, the shear stability and the rolling friction coefficient (MTM friction coefficient) are deteriorated. Also, if the weight ratio (c / a) exceeds 0.00300, the solubility of the copolymer (A) in the base oil is deteriorated.

[0070] In the copolymer (A), the weight proportion of the monomer (d) among the constituent monomers of the copolymer (A) is preferably 45 to 85% by weight, more preferably 55 to 80% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoints of the HTHS viscosity at 100°C, the kinematic viscosity at 40°C, the shear stability, the rolling friction coefficient (MTM friction coefficient) and the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (e) among the constituent monomers of the copolymer (A) is preferably 1 to 53% by weight, more preferably 1 to 35% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoints of the HTHS viscosity at 100°C, the kinematic viscosity at 40°C, the shear stability, the rolling friction coefficient (MTM friction coefficient) and the viscosity index improving effect.

[0071] In the copolymer (A), the weight proportion of the monomer (f) among the constituent monomers of the copolymer (A) is preferably 50% by weight or less, and more preferably 1 to 40% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the effect of improving the HTHS viscosity and viscosity index at the effective temperature. In the copolymer (A), the weight proportion of the monomer (g) among the constituent monomers of the copolymer (A) is preferably 40% by weight or less, and more preferably 1 to 30% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the effect of improving the HTHS viscosity and viscosity index at the effective temperature. In the copolymer (A), the weight proportion of the monomer (h) among the constituent monomers of the copolymer (A) is preferably 30% by weight or less, and more preferably 1 to 20% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the effect of improving the HTHS viscosity and viscosity index at the effective temperature. In the copolymer (A), the weight proportion of the monomer (i) among the constituent monomers of the copolymer (A) is preferably 20% by weight or less, and more preferably 1 to 15% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the effect of improving the HTHS viscosity and viscosity index at the effective temperature. In the copolymer (A), the weight proportion of the monomer (j) among the constituent monomers of the copolymer (A) is preferably 10% by weight or less, and more preferably 1 to 5% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the HTHS viscosity at the effective temperature. In the copolymer (A), the weight proportion of the monomer (k) among the constituent monomers of the copolymer (A) is preferably 5% by weight or less, and more preferably 0.5 to 2% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (l) among the constituent monomers of the copolymer (A) is preferably 20% by weight or less, and more preferably 1 to 10% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (m) among the constituent monomers of the copolymer (A) is preferably 5% by weight or less, and more preferably 0.1 to 2% by weight, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the viscosity index improving effect. In the copolymer (A), the weight proportion of the monomer (n) among the constituent monomers of the copolymer (A) is preferably 1 weight % or less, and more preferably 0.01 to 0.5 weight %, based on the total weight of the monomers constituting the copolymer (A), from the viewpoint of the viscosity index improving effect.

[0072] The Mw of the copolymer (A) is preferably 5,000 to 2,000,000, more preferably 5,000 to 1,000,000, more preferably 10,000 to 800,000, particularly preferably 15,000 to 700,000, most preferably 30,000 to 600,000, and most preferably 150,000 to 550,000. When the Mw of the copolymer (A) is 5,000 or more, the effect of improving the viscosity temperature characteristic and the effect of improving the viscosity index tend to be good. In addition, the amount of the viscosity index improver added is not too large, which is advantageous in terms of cost. When it is 2,000,000 or less, the shear stability tends to be good.

[0073] The more preferred range of Mw of the copolymer (A) varies depending on the application of the viscosity index improver and the lubricating oil composition, and is shown in Table 2.

[0074] [Table 2]

[0075] The Mn of the copolymer (A) is preferably 2,500 or more, more preferably 5,000 or more, particularly preferably 7,500 or more, and most preferably 15,000 or more. Also, it is preferably 300,000 or less, more preferably 150,000 or less, and particularly preferably 100,000 or less. When Mn is 2,500 or more, the viscosity temperature characteristic and viscosity index tend to be improved. Also, the amount of viscosity index improver added is not too large, which is advantageous in terms of cost. When Mn is 300,000 or less, shear stability tends to be good. The molecular weight distribution (Mw / Mn) of the copolymer (A) is preferably from 1.0 to 4.0, more preferably from 1.5 to 3.5, from the viewpoint of shear stability. The conditions for measuring Mw, Mn and molecular weight distribution of the copolymer (A) are the same as those for measuring Mw and Mn of the monomer (a).

[0076] The copolymer (A) can be obtained by a known production method, specifically, a method of solution polymerization of the above-mentioned monomers in a solvent in the presence of a polymerization catalyst can be mentioned. Examples of the solvent include toluene, xylene, ethyl acetate, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, mineral oil, synthetic oil, and mixtures thereof. Examples of the polymerization catalyst include azo catalysts (2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile), etc.), peroxide catalysts (benzoyl peroxide, cumyl peroxide, lauryl peroxide, etc.), and redox catalysts (mixtures of benzoyl peroxide and tertiary amines, etc.). Furthermore, if necessary, a known chain transfer agent (such as an alkyl mercaptan having 2 to 20 carbon atoms) can be used to adjust the molecular weight. The polymerization temperature is preferably 25 to 140° C., more preferably 50 to 120° C. In addition to the above solution polymerization, the copolymer (A) can also be obtained by bulk polymerization, emulsion polymerization or suspension polymerization. The polymerization form of the copolymer (A) may be either a random addition polymer or an alternating copolymer, and may also be either a graft copolymer or a block copolymer.

[0077] The SP value calculated based on the weight fraction of the monomers constituting the copolymer (A) is 8.0 to 10.0 (cal / cm3) from the viewpoint of solubility in the base oil. 3 ) 1 / 2 is preferable, and more preferably 8.5 to 9.5 (cal / cm 3 ) 1 / 2 and particularly preferably 8.7 to 9.4 (cal / cm 3 ) 1 / 2 and most preferably 8.8 to 9.3 (cal / cm 3 ) 1 / 2 It is. The SP value calculated based on the weight fraction of the monomers constituting copolymer (A) (sometimes abbreviated as the SP value of copolymer (A)) refers to the SP value of the constituent units (structures in which vinyl groups have become single bonds through polymerization) derived from each monomer constituting copolymer (A) calculated using the above-mentioned SP value calculation method, and the arithmetic average based on the weight fraction of each constituent monomer at the time of charging. For example, when the monomer is methyl methacrylate, the constituent unit derived from methyl methacrylate has two CH3, one CH2, one C, and one CO2 as atomic groups, so that the SP value of the constituent unit derived from methyl methacrylate is 9.933 (cal / cm) according to the following formula: 3 ) 1 / 2 Similarly, the SP value of the structural unit derived from ethyl methacrylate is 9.721 (cal / cm 3 ) 1 / 2 It can be seen that. ΣΔe i =1125×2+1180+350+4300=8080 ΣΔv i =33.5×2+16.1-19.2+18.0=81.9 δ=(8080 / 81.9) 1 / 2 =9.933(cal / cm 3 ) 1 / 2 When the copolymer is a polymer of 50% by weight of methyl methacrylate and 50% by weight of ethyl methacrylate, the SP value of the copolymer is calculated by taking the arithmetic average based on the weight fraction of the SP values ​​of the constituent units derived from each monomer, as shown below. Copolymer SP value = (9.933 x 50 + 9.721 x 50) / 100 = 9.827 The SP value calculated based on the weight fraction of the monomers constituting the copolymer (A) can be adjusted to a desired range by appropriately adjusting the monomers used and the weight fractions of each monomer used. Specifically, the SP value can be reduced by using a large amount of monomers with a large number of carbon atoms in the alkyl group, and the SP value can be increased by using a large amount of monomers with a small number of carbon atoms in the alkyl group.

[0078] The viscosity index improver of the present invention may contain, in addition to the above-mentioned copolymer (A), a (meth)acrylic acid alkyl ester (co)polymer (B) other than the copolymer (A), and it is preferable for the viscosity index improver to contain the (co)polymer (B) from the viewpoint of low-temperature viscosity. The (co)polymer (B) includes a (co)polymer that does not contain the monomer (a), and examples thereof include a (co)polymer that contains, as a constituent monomer, a (meth)acryloyl monomer (e) having a linear or branched alkyl group having 9 to 36 carbon atoms. Specific examples thereof include n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate copolymers, n-octadecyl (meth)acrylate / n-dodecyl (meth)acrylate (molar ratio 10-30 / 90-70) copolymers, n-tetradecyl (meth)acrylate / n-dodecyl (meth)acrylate (molar ratio 10-30 / 90-70) copolymers, n-hexadecyl (meth)acrylate / n-dodecyl (meth)acrylate / methyl (meth)acrylate (molar ratio 20-40 / 55-75 / 0-10) copolymers and n-dodecyl acrylate / n-dodecyl methacrylate (molar ratio 10-40 / 90-60) copolymers, which may be used alone or in combination of two or more.

[0079] The content of the (co)polymer (B) in the viscosity index improver of the present invention is preferably 0.01 to 30% by weight, more preferably 0.01 to 10% by weight, based on the weight of the copolymer (A) from the viewpoint of low-temperature viscosity.

[0080] The Mw of the (co)polymer (B) is preferably from 5,000 to 100,000, and more preferably from 10,000 to 80,000, from the viewpoint of decreasing the pour point temperature. The SP value calculated based on the weight fraction of the monomers constituting the (co)polymer (B) is preferably from 7.0 to 10, and more preferably from 8.0 to 9.5, from the viewpoint of solubility in the base oil. The conditions for measuring the Mw of the (co)polymer (B) are the same as those for measuring the Mw of the above-mentioned monomer (a), and the method for calculating the SP value is the same as for the copolymer (A).

[0081] In the present invention, the viscosity index improver is only required to contain the copolymer (A), and may contain a base oil from the viewpoint of handling properties. Examples of base oils include mineral oils (solvent refined oils, paraffin oils, high viscosity index oils containing isoparaffin, high viscosity index oils obtained by hydrocracking isoparaffin, and naphthenic oils), synthetic lubricating oils (hydrocarbon synthetic lubricating oils (poly-α-olefin synthetic lubricating oils, etc.) and ester synthetic lubricating oils (such as ester oils described below), etc.), and mixtures thereof. Among these, mineral oils are preferred from the viewpoint of compatibility with components. From the viewpoints of viscosity index improving effect and low temperature viscosity, the viscosity index improver of the present invention preferably contains 10% by weight or more and 40% by weight or less of the copolymer (A) based on the weight of the viscosity index improver. In the viscosity index improver of the present invention, the (co)polymer (B) is preferably contained in an amount of 0.01 to 5% by weight based on the weight of the viscosity index improver, from the viewpoint of low-temperature viscosity.

[0082] <Lubricating oil composition> The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and a base oil, and may further contain at least one additive selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, pour point depressants, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, metal deactivators, and corrosion inhibitors. From the viewpoint of fuel economy, the lubricating oil composition of the present invention preferably contains 0.1% by weight or more and less than 10% by weight of copolymer (A) based on the weight of the lubricating oil composition, and more preferably 0.5% by weight or more and less than 10% by weight. From the viewpoint of low temperature viscosity, the lubricating oil composition of the present invention preferably contains the (co)polymer (B) in an amount of 0.01 to 2% by weight based on the weight of the lubricating oil composition. In the lubricating oil composition of the present invention, the content of the (co)polymer (B) is preferably 0.01 to 30% by weight, more preferably 0.01 to 10% by weight, based on the weight of the copolymer (A), from the viewpoint of low temperature viscosity. From the viewpoint of fuel economy, the content of the base oil in the lubricating oil composition of the present invention is preferably 1 to 99.9 wt %, and more preferably 90 to 99.5 wt %, based on the weight of the lubricating oil composition.

[0083] The kinematic viscosity of the base oil in the lubricating oil composition at 100°C is 1 to 15 mm from the viewpoint of the viscosity index and the HTHS viscosity at the operating temperature. 2 / s is preferable, and 2 to 5 mm 2 / s.

[0084] When the lubricating oil composition is used as an engine oil, the kinetic viscosity at 100°C is 2 to 10 mm 2 Preferably, the base oil of the oil composition contains 1% by weight or more and less than 10% by weight of the copolymer (A). When the lubricating oil composition is used as a gear oil, the kinetic viscosity at 100°C is 2 to 10 mm 2 Preferably, the base oil of the oil composition contains 3 to 20% by weight of the copolymer (A). When the lubricating oil composition is used as an automatic transmission fluid (ATF, belt-CVTF, etc.), the kinetic viscosity at 100°C is 2 to 6 mm 2 Preferably, the base oil of the oil composition contains 3 to 20% by weight of the copolymer (A). When the lubricating oil composition is used as a traction oil, the kinetic viscosity at 100°C is 1 to 5 mm 2 Preferably, the base oil of the oil composition contains 0.5 to 10% by weight of the copolymer (A).

[0085] The lubricating oil composition of the present invention may contain various additives, including at least one additive selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, pour point depressants, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, metal deactivators, and corrosion inhibitors, and specific examples thereof include the following: (1) Detergent: Basic, overbased or neutral metal salts [such as overbased or alkaline earth metal salts of sulfonates (such as petroleum sulfonates, alkylbenzene sulfonates and alkylnaphthalene sulfonates)], salicylates, phenates, naphthenates, carbonates, phosphonates and mixtures thereof; (2) Dispersant: Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products and borates, etc.; (3) Antioxidants: Hindered phenols and aromatic secondary amines, etc.; (4) Oiliness enhancer: Long-chain fatty acids and their esters (such as oleic acid and oleic acid esters), long-chain amines and their amides (such as oleylamine and oleylamide), etc.; (5) Pour point depressants Polyalkyl methacrylate, ethylene-vinyl acetate copolymer, etc.; (6) Friction and wear modifier: Molybdenum and zinc compounds (molybdenum dithiophosphate, molybdenum dithiocarbamate, zinc dialkyldithiophosphate, etc.); (7) Extreme pressure agents: Sulfur compounds (monosulfides or disulfides, sulfoxides and sulfur phosphide compounds), phosphide compounds and chlorine compounds (chlorinated paraffins, etc.); (8) Defoaming agent: Silicone oils, metal soaps, fatty acid esters and phosphate compounds, etc.; (9) Demulsifier: Quaternary ammonium salts (such as tetraalkylammonium salts), sulfated oils and phosphates (such as phosphates of polyoxyethylene-containing nonionic surfactants), hydrocarbon solvents (toluene, xylene, ethylbenzene), etc.; (10) Metal deactivators Nitrogen atom-containing compounds (benzotriazole, etc.), nitrogen atom-containing chelate compounds (N,N'-disalicidene-1,2-diaminopropane, etc.), nitrogen and sulfur atom-containing compounds (2-(n-dodecylthio)benzimidazole, etc.), etc.; (11) Corrosion inhibitors: Nitrogen atom-containing compounds (such as benzotriazole and 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate).

[0086] These additives may be added alone or in combination of two or more additives as required. In addition, a combination of these additives, sometimes called a performance additive or a package additive, may be added. The content of each of these additives is preferably 0.1 to 15% by weight based on the total weight of the lubricating oil composition, and the total content of the additives is preferably 0.1 to 30% by weight, more preferably 0.3 to 20% by weight, based on the total weight of the lubricating oil composition.

[0087] The lubricating oil composition of the present invention is suitably used for gear oils (differential oils, industrial gear oils, etc.), MTFs, transmission fluids [ATF, DCTF, belt-CVTF, etc.], traction oils (toroidal-CVTF, etc.), shock absorber oils, power steering oils, hydraulic oils (construction machinery hydraulic oils, industrial hydraulic oils, etc.) and engine oils (for gasoline and diesel). EXAMPLES

[0088] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.

[0089] <Production Example 1> In a SUS pressure-resistant reaction vessel equipped with a temperature controller and a stirrer, 400 parts by weight of degassed and dehydrated hexane, 1 part by weight of tetrahydrofuran, 75 parts by weight of 1,3-butadiene, and 2 parts by weight of n-butyllithium were charged, and then polymerization was carried out at a polymerization temperature of 70°C. After the polymerization rate reached nearly 100%, 2 parts by weight of ethylene oxide was added and reacted at 50° C. for 3 hours. To terminate the reaction, 50 parts by weight of water and 25 parts by weight of 1N hydrochloric acid solution were added and stirred at 80° C. for 1 hour. The organic phase of the reaction solution was recovered in a separatory funnel and heated to 70° C., after which the solvent was removed under reduced pressure of 0.027 to 0.040 MPa over 2 hours. The obtained polybutadiene having a hydroxyl group at one end was transferred to a reaction vessel equipped with a temperature control device, a stirrer, and a hydrogen inlet tube, and 150 parts by weight of tetrahydrofuran was added to dissolve it uniformly. A suspension of 10 parts by weight of palladium carbon and 50 parts by weight of tetrahydrofuran was poured therein, and then the mixture was reacted at room temperature for 8 hours while hydrogen was supplied into the liquid from the hydrogen inlet tube at a flow rate of 30 mL / min. The palladium carbon was then removed by filtration, and the obtained filtrate was heated to 70°C and tetrahydrofuran was removed under a reduced pressure of 0.027 to 0.040 MPa to obtain a hydrogenated polybutadiene having a hydroxyl group at one end (Y1-1) (total ratio of isobutylene groups and 1,2-butylene groups: 45 mol%, 1,2-adduct / 1,4-adduct (molar ratio): 45 / 55, hydroxyl value: 8.0 mgKOH / g, crystallization temperature: -60°C or less). 245 parts by weight of hydrogenated polybutadiene polymer containing a hydroxyl group at one end (Y1-1), 245 parts by weight of methacrylic acid, and 98 parts by weight of sulfonic acid group-supported inorganic porous material (acid value 45 mg KOH / g, particle size 240 μm) were added, and esterification was carried out at 120°C. Next, the sulfonic acid group-supported inorganic porous material was removed by filtration, and the reaction liquid was subjected to reduced pressure (0.027 to 0.040 MPa) to remove excess methacrylic acid, thereby obtaining monomer (a-1). The molecular weight of the obtained (a-1) was measured by GPC, and the ratio of 1,2-butylene groups was 13 The results were Mw=6,900, Mn=6,800, the ratio of 1,2-butylene groups in the general formula (1)=45 mol%, -X 1 - is a group represented by -O(CH2CH2O)1-, and p=0.

[0090] <Production Example 2> In a 1L SUS pressure-resistant reaction vessel equipped with a temperature controller and a stirrer, 400 parts by weight of degassed and dehydrated hexane, 1 part by weight of tetrahydrofuran, and 0.4 parts by weight of n-butyllithium were charged, and then cooled to -40°C. 90 parts by weight of 1,3-butadiene liquefied at -40°C was added thereto, and polymerization was carried out at a polymerization temperature of -40°C. Thereafter, the same procedure as in Production Example 1 was carried out to obtain a hydrogenated polybutadiene polymer (Y1-2) containing a hydroxyl group at one end (total ratio of isobutylene groups and 1,2-butylene groups: 65 mol%, 1,2-adduct / 1,4-adduct (molar ratio): 65 / 35, hydroxyl value: 13.1 mgKOH / g, crystallization temperature: -60°C or less). Furthermore, (Y1-2) was esterified with methacrylic acid to obtain a monomer (a-2). The molecular weight of the obtained (a-2) was measured by GPC, and the ratio of 1,2-butylene groups was 13 The results were Mw=6,900, Mn=6,800, the ratio of 1,2-butylene groups=65 mol%, and -X in the general formula (1). 1 - is a group represented by -O(CH2CH2O)1-, and p=0.

[0091] <Example 1> In a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a nitrogen inlet tube, 200 parts by weight of the polymerization base oil and 100 parts by weight of the monomer blend shown in Table 3 were added, and nitrogen replacement (gas phase oxygen concentration 100 ppm) was performed. The temperature was raised to 76°C while stirring under sealing, and then the amount of initiator shown in Table 3 was added and polymerization reaction was performed at the same temperature for 4 hours. After raising the temperature to 90°C and reacting for 2 hours, 0.05 parts by weight of 2,2'-azobis(2-methylbutyronitrile) was added relative to the monomer blend. After raising the temperature to 120 to 130°C, the dilution base oil shown in Table 3 was added here to obtain a viscosity index improver (R-1) containing the copolymer (A-1). The SP value of the obtained copolymer (A-1) was calculated by the above method, and Mw was measured by the above method. The results are shown in Table 3.

[0092] <Examples 2 to 10, Comparative Examples 1 to 2> The same procedure as in Example 1 was followed except that the monomer blend, base oil for polymerization and dilution, and amount of initiator were as shown in Table 3, to obtain viscosity index improvers (R-2 to R-10, S-1 to S-2) containing copolymers.

[0093] [Table 3]

[0094] The compositions of the monomers (a) to (d) shown in Table 3 are as follows. (a-1): Methacrylic acid ester of (Y1-1) [Mn: 6800] (a-2): Methacrylic acid ester of (Y1-2) [Mn: 6800] (b-1): Ethoxyethyl methacrylate (b-2): n-butoxyethyl methacrylate (c-1): Cyclohexanedimethanol dimethacrylate (c-2): Tricyclodecane dimethanol diacrylate (c-3): Cyclohexanedimethanol diacrylate (d-1): Methyl methacrylate (d-2): Ethyl methacrylate (d-3): n-butyl methacrylate (e-1): n-dodecyl methacrylate (e-2): Methacrylic acid ester of a mixture of linear and branched alkyl methacrylates having 12 to 13 carbon atoms (a mixture of NEODOL23 (weight ratio: linear C12: branched C12: linear C13: branched C13 = 40:10:40:10) manufactured by SHELL) (e-3): Methacrylic acid ester of a mixture of linear and branched alkyl methacrylates having 14 to 15 carbon atoms (a mixture of NEODOL45 manufactured by SHELL (weight ratio = linear C14: branched C14: linear C15: branched C15 = 40:10:40:10)). (e-4): n-hexadecyl methacrylate (e-5): n-octadecyl methacrylate

[0095] The SP values ​​of the constitutional units (structures in which carbon-carbon double bonds have reacted to form single bonds) derived from each of the monomers (a-1), (a-2), (e-2), and (e-3) were calculated based on the following formula. Structural unit derived from (a-1) ΣΔe i =1125(CH3)+1180(CH2)+350(C)+4300(CO2)=6955 ΣΔv i =33.5(CH3)+16.1(CH2)-19.2(C)+18.0(CO2)=48.4 ΣΔe i =1180(CH2)×2+800(O)=3160 ΣΔv i = 16.1(CH2) x 2 + 3.8(O) = 36 ΣΔe i =1180(CH2)×2+1125(CH3)+820(CH)=4305 ΣΔv i =16.1(CH2)×2+33.5(CH3)-1.0(CH)=64.7 ΣΔe i =1180(CH2)×4=4720 ΣΔv i =16.1(CH2)×4=64.4 Here, the total number of 1,2-butylene groups and 1,4-butylene groups is as follows. Total number of 1,2-butylene groups and 1,4-butylene groups = (6800 - 85 - 44) / 56 = 119.125 Therefore, the parameters of the constitutional unit derived from (a-1) are as follows: ΣΔe i =6955+3160+4305×119.125×0.45+4720×119.125×0.55=550138.4 ΣΔv i =48.4+36+64.7×119.125×0.45+64.4×119.125×0.55=7772.132 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(550138.4 / 772.132)1 / 2 =8.413

[0096] Structural unit derived from (a-2) Total number of 1,2-butylene groups and 1,4-butylene groups = (6800 - 85 - 44) / 56 = 119.125 ΣΔe i =6955+3160+4305×119.125×0.65+4720×119.125×0.35=540251 ΣΔv i =48.4+36+64.7×119.125×0.65+64.4×119.125×0.35=7779.279 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(540251 / 7779.279) 1 / 2 =8.334

[0097] (e-2) derived structural unit Linear C12 ΣΔe i =6955+1180×11+1125=21060 ΣΔv i =48.4+16.1×11+33.5=259 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(21060 / 259) 1 / 2 =9.017 Branch C12 ΣΔe i =6955+1180×9+1125×2+820=20645 ΣΔv i =48.4+16.1×9+33.5×2-1.0=259.3 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(20645 / 259.3) 1 / 2 =8.923 Linear C13 ΣΔe i =6955+1180×12+1125=22240 ΣΔv i=48.4+16.1×12+33.5=275.1 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(22240 / 275.1) 1 / 2 =8.991 Branch C13 ΣΔe i =6955+1180×10+1125×2+820=21825 ΣΔv i =48.4+16.1×10+33.5×2-1.0=275.4 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(21825 / 275.4) 1 / 2 =8.902 SP value of the constituent unit derived from (e-2) = (9.017 x 40 + 8.923 x 10 + 8.991 x 40 + 8.902 x 10) / 100 = 8.986

[0098] (e-3) derived structural unit Linear C14 ΣΔe i =6955+1180×13+1125=23420 ΣΔv i =48.4+16.1×13+33.5=291.2 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(23420 / 291.2) 1 / 2 =8.968 Branch C14 ΣΔe i =6955+1180×11+1125×2+820=23005 ΣΔv i =48.4+16.1×11+33.5×2-1.0=291.5 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(23005 / 291.5) 1 / 2 =8.884 Linear C15 ΣΔe i=6955+1180×14+1125=24600 ΣΔv i =48.4+16.1×14+33.5=307.3 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(24600 / 307.3) 1 / 2 =8.947 Branch C15 ΣΔe i =6955+1180×12+1125×2+820=24185 ΣΔv i =48.4+16.1×12+33.5×2-1.0=307.6 SP value = (ΣΔe i / ΣΔv i ) 1 / 2 =(24185 / 307.6) 1 / 2 =8.867 SP value of the constituent unit derived from (e-3) = (8.968 x 40 + 8.884 x 10 + 8.947 x 40 + 8.867 x 10) / 100 = 8.941

[0099] The base oils shown in Tables 3 and 4 were as follows: Hydrocarbon oil-1: SK Lubricants, product name "Yubase4", API classification Group III (kinetic viscosity at 100°C: 4.21 mm 2 / s, kinematic viscosity at 40°C: 19.12mm 2 / s) Hydrocarbon oil-2: SK Lubricants, product name "Yubase3", API classification Group III (kinetic viscosity at 100°C: 3.06 mm 2 / s, kinematic viscosity at 40°C: 12.25mm 2 / s) GTL oil-1: Shell XHVI4, kinematic viscosity at 100°C: 4.08mm 2 / s, kinematic viscosity at 40°C: 18.22mm 2 / s GTL oil-2: Shell Ondina X415, kinematic viscosity at 100°C: 2.70mm 2 / s, kinematic viscosity at 40℃: 9.80mm 2 / s CTL oil-1: Shanxi Lu'an Taihang Lubricant Technology Co., Ltd., ICCSYN3, kinematic viscosity at 100°C: 2.96mm 2 / s, kinematic viscosity at 40°C: 11.20mm 2 / s Ester oil-1: API classification Group V (bis(2-ethylhexyl) sebacate, kinematic viscosity at 100°C: 3.23 mm 2 / s, kinematic viscosity at 40°C: 11.53mm 2 / s)

[0100] <Examples 11 to 20 and Comparative Example 3 (Evaluation as 0W-16 grade)> In a stainless steel vessel equipped with a stirrer, add hydrocarbon oil-1 (Yubase 4 (kinematic viscosity at 100°C: 4.21 mmHg)) to the mixture shown in Table 4. 2 / s, kinematic viscosity at 40°C: 19.12mm 2 / s)) and Hydrocarbon Oil-2 (Yubase3 (3.06 mm 2 / s, kinematic viscosity at 40°C: 12.25mm 2 The lubricating oil composition obtained had a kinetic viscosity of 6.5 mm at 100°C. 2 Viscosity index improvers (R-1) to (R-10) and (S-1) were added so that the viscosity index per unit volume and NOACK evaporation rate were 22%, respectively, to obtain lubricating oil compositions (V-1) to (V-10) and (W-1). The shear stability, HTHS viscosity (150°C, 100°C), kinematic viscosity (40°C, 100°C), viscosity index, MTM friction coefficient, and solubility in additive-containing base oil of the lubricating oil compositions (V-1) to (V-10) and (W-1) were measured by the following methods. The results are shown in Table 4. The viscosity index improver (S-2) is a hydrocarbon oil-1 (Yubase 4 (kinetic viscosity at 100°C: 4.21 mm 2 / s, kinematic viscosity at 40°C: 19.12mm 2 / s)) and Hydrocarbon Oil-2 (Yubase3 (3.06 mm 2 / s, kinematic viscosity at 40°C: 12.25mm 2 / s)) and an engine oil additive package (Infineum P-5741, 10% by weight of the total) and therefore could not be evaluated.

[0101] [Table 4]

[0102] <Method for measuring HTHS viscosity of lubricating oil composition> Measured at 150°C and 100°C according to the method of ASTM D 4683.

[0103] <Method of measuring viscosity of lubricating oil composition> The kinematic viscosity was measured at 40°C and 100°C according to the method of JIS-K2283 (2000), and the viscosity index was calculated according to the method of JIS-K2283 (2000). The higher the viscosity index value, the higher the effect of improving the viscosity index.

[0104] <Methods for measuring and calculating the shear stability of lubricating oil compositions> Measured using the ultrasonic method (low output method) of JPI-5S-29-2006. The smaller the value, the higher the shear stability.

[0105] <Rolling friction characteristics - MTM friction coefficient> Equipment:PCS Instruments MTM-2 Disc: MTM polished disc (standard) (0.01 micron) Ball: Drilled 3 / 4 AISI52100 precision steel ball Speed: 10mm / s~3,000mm / s Temperature: 100℃ Sliding / rolling ratio: 50% Load: 30N As a result of the friction evaluation, a Stribeck curve was obtained, and the friction coefficient at a speed of 10 mm / s was measured.

[0106] <Method for evaluating the solubility of copolymers in additive-containing base oils> The appearance of the lubricating oil compositions (V-1) to (V-10) and (W-1) was visually observed, and the base oil solubility was evaluated according to the following evaluation criteria. [Evaluation Criteria] ○: The appearance is uniform and there is no insoluble matter. ×: The appearance is non-uniform and insoluble matter is observed.

[0107] As is clear from the results in Table 4, when the copolymer (A) containing the polyolefin monomer (a) represented by the general formula (1) and the polyfunctional monomer (c) having two or more ethylenically unsaturated groups in one molecule as essential constituent monomers has a weight ratio (c / a) of the monomer (c) to the weight of the monomer (a) in the monomers constituting the copolymer (A) of 0.00001 to 0.00300, it has excellent shear stability when added to a lubricating oil composition. Furthermore, it is found that the MTM friction coefficient is low. [Industrial Applicability]

[0108] The lubricating oil composition containing the viscosity index improver of the present invention has extremely high shear stability and can be suitably used in gear oils (differential oils and industrial gear oils, etc.), MTFs, transmission fluids [ATF, DCTF, belt-CVTF, etc.], traction oils (toroidal-CVTF, etc.), shock absorber oils, power steering oils, hydraulic oils (construction machinery hydraulic oils and industrial hydraulic oils, etc.) and engine oils (gasoline and diesel), and can be particularly suitably used as a lubricating oil composition for internal combustion engines, in particular as a lubricating oil composition for hybrid vehicles.

Claims

1. A viscosity index improver comprising a copolymer (A) having, as essential constituent monomers, a polyolefin monomer (a) represented by the following general formula (1) and a polyfunctional monomer (c) having two or more ethylenically unsaturated groups in one molecule, wherein the weight ratio (c / a) of the monomer (c) to the weight of the monomer (a) among the monomers constituting the copolymer (A) is 0.00001 to 0.00300. 【Chemistry 1】 [In general formula (1), R １ is a hydrogen atom or a methyl group; １ - is -O-, -O (AO) ｍ - or -NH-, where A is an alkylene group having 2 to 4 carbon atoms, m is an integer from 1 to 10, and when m is 2 or more, A may be the same or different; R ２ is a residue obtained by removing one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit; and p is the number 0 or 1.

2. The viscosity index improver according to claim 1, wherein the copolymer (A) is a copolymer containing, as constituent monomers, a monomer (b) represented by the following general formula (2), a (meth)acrylic acid alkyl ester monomer (d) having an alkyl group having 1 to 4 carbon atoms, and a (meth)acryloyl monomer (e) having an alkyl group having 9 to 36 carbon atoms: 【Chemistry 2】 [In the general formula (2), R ３ is a hydrogen atom or a methyl group; ２ - is a group represented by -O- or -NH-; R ４ is an alkylene group having 2 to 4 carbon atoms; R ５ is an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms; q is an integer from 1 to 20, and when q is 2 or more, R ４ may be the same or different.

3. The viscosity index improver according to claim 2, wherein the copolymer (A) is a copolymer containing, based on the total weight of the monomers constituting (A) as constituent monomers, 1 to 20% by weight of the monomer (a), 1 to 35% by weight of the monomer (b), 0.00001 to 0.060% by weight of the monomer (c), 45 to 85% by weight of the monomer (d), and 1 to 53% by weight of the monomer (e).

4. The solubility parameter of the copolymer (A) is 8.0 to 10.0 (cal / cm ３ ) １／２ 2. The viscosity index improver of claim 1 .

5. 2. The viscosity index improver according to claim 1, wherein the weight average molecular weight of the copolymer (A) is 5,000 to 2,000,000.

6. A lubricating oil composition comprising the viscosity index improver according to any one of claims 1 to 5 and a base oil.

7. The base oil has a kinetic viscosity of 1 to 15 mm at 100°C. ２ 7. The lubricating oil composition according to claim 6, wherein the viscosity index of the base oil is 100 or greater.

8. The lubricating oil composition according to claim 6, further comprising at least one additive selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, pour point depressants, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, metal deactivators and corrosion inhibitors.

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